(a) Technical Field
The present invention relates to a thermal management system (TMS) for a fuel cell vehicle. More particularly, the present invention relates to a heating device with cathode oxygen depletion (COD) function for a fuel cell vehicle, in which an existing COD and a heating device for improving cold startability of the fuel cell vehicle are integrated.
(b) Background Art
Automobile companies have developed hydrogen fuel cell vehicles with keen interest for the purpose of development of environment-friendly vehicles. The hydrogen fuel cell vehicles developed so far have numerous problems to be solved and one of the most important and difficult problems is to provide improved cold startability.
One of the solutions for improving the cold startability of the conventional fuel cell vehicle is rapid thawing of pure water using a heater provided in a rapid thaw accumulator (RTA).
However, if the pure water is used, there are many problems that the pure water is frozen at a temperature below the freezing point, a coolant loop thereof is complicated, and a drain valve is required to be provided additionally.
To solve such problems, there was proposed a method in which an antifreeze solution for the use in a stack is used as a coolant and the coolant is rapidly heated to improve the power generation efficiency of the stack at a temperature below the freezing point.
For this, it is necessary to attach the heater to a coolant line of the stack. Moreover, in order to prevent deterioration of durability of the stack due to corrosion of catalyst-loaded carbon during start-up and shut-down of the fuel cell vehicle, a COD is connected to both terminals of the stack so that the electric energy generated by a chemical reaction between hydrogen and oxygen is consumed to generate heat energy.
FIG. 1 is a diagram illustrating the operation principle of the conventional COD, in which VLD100A and VLD100B are start-up CODs, and VLD110 is a shut-down COD. The VLD100A and VLD100B are connected to an end of a stack module via a relay and a fuse, and the VLD110 is connected to ends of two stack modules via two relays and two fuses.
Upon start-up of the vehicle, the VLD100A and VLD100B are connected to the stack to cause a reaction between hydrogen remaining in the stack and oxygen to generate heat and, during shut-down of the vehicle, the VLD110 is connected to the stack to remove the hydrogen remaining in the stack.
Especially, during shut-down, the engine is completely turned off by a normally close (N/C) relay (not shown) attached thereto, and the shut-down COD is always connected to both ends of the stack even in the case where the vehicle is stopped.
However, conventionally, there has been no heater developed specially for the purpose of heating the stack coolant to improve the power generation efficiency of the stack at a temperature below the freezing point after start-up of the vehicle. Moreover, the conventional COD is not used as a heater but used as a device for ensuring durability of the stack by generating heat using the hydrogen remaining in the stack and oxygen during start-up or shut-down of the vehicle.
Accordingly, in addition to the above COD, it is required to provide a heater for rapidly heating the coolant in order to improve the power generation efficiency of the stack at a temperature below the freezing point after start-up of the vehicle. However, in a case where the heater for heating the coolant is provided separately from the COD, there are drawbacks that the manufacturing cost of the vehicle is increased and it is difficult to ensure a layout space.
Meanwhile, as shown in FIG. 2, start-up CODs 103 and shut-down CODs 104 are provided at both ends of a cylindrical housing 100, and a coolant inlet 101 and an outlet 102 are formed at both ends of the housing 100. Since the cylindrical housing 100 has an inner diameter greater than that of the coolant inlet 101 and the outlet 102, the coolant passes through sudden expansion and sudden contraction pipes while flowing from the coolant inlet 101 to the outlet 102, and thus there is a significant pressure drop, which results in a heavy load being applied to a pump.
Moreover, the conventional COD has a drawback in that since it is attached to the front coolant line, it is impossible to perform maintenance and repair without using a lift. And, since the heater may be exposed to the air, the heat generated from the heater may be lost.
To solve the above problems, the inventors of the present invention proposed a heater with a COD function for a fuel cell vehicle as is disclosed in Korean Patent Application No. 10-2007-0105369, in which a heater for improving cold startability of the fuel cell vehicle and an existing COD function for ensuring durability of a fuel cell stack are integrated so as to reduce the manufacturing cost of the vehicle, ensure a layout space, improve maintenance efficiency, and improve the cold startability through a multistage current control.
However, since a cartridge heater provided inside a housing of the above heater, in which the heater for improving the cold startability of the fuel cell vehicle and the existing COD function are integrated, has a calorific value of about 3.2 kW per unit, a high heat density, bubbles are uniformly formed on the overall heater surface when the flux of the coolant is 0 LPM, as shown in FIG. 3.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.